man, i'm talking about complex systems (2G+ of source code for example) that are already well past several low-hanging-fruit passes, component- and system-wise.

man, i'm talking about complex systems (2G+ of source code for example) that are already well past several low-hanging-fruit passes, component- and system-wise. Their performance after that reflects the overall average emphasis on performance and skills of developers through the life of the project. And no amount of after-the-fact optimization would make Windows into Linux performance-wise.